It is well known that contact lenses can be used to improve vision. Various contact lenses have been commercially produced for many years. Hydrogel contact lenses are very popular today. These lenses are often more comfortable to wear than contact lenses made of hard materials. Malleable soft contact lenses can be manufactured by forming a lens in a multi-part mold where the combined parts form a topography consistent with the desired final lens. Contact lenses made from silicone hydrogels have been disclosed. However, many of the raw materials which are used to make silicone hydrogel contact lenses have impurities which cannot be efficiently removed using the conventional water and saline based leaching steps.
Some early disclosed methods used only water. However, these early processes used extremely long water leaching and/or high temperatures to extract undesirable components. No clinical data on the resulting lenses is available to confirm removal of undesirable impurities.
Processes for removing undesired impurities from silicone hydrogel lenses via leaching steps using alcohols have been disclosed. The alcohols can sting the eye and must be completely removed from the contact lens. Special handling steps must be taken to dispose of the alcohols making the manufacturing process more expensive. Moreover, the use of organic solutions can present drawbacks, including, for example: safety hazards; increased risk of down time to a manufacturing line; high cost of release solution; and the health hazards associated with organic solvents.
While modifying the leaching process is possible, it would be desirable to find silicone hydrogel materials which are free of impurities which cause undesirable ocular reactions, such as stinging.